In a maintenance work of a wind turbine generator, there is a work necessary to separate a nacelle and a tower. As such a maintenance work, for example, there are an exchange of a yaw rotation bearing or bearing seal, an adjustment of a shim attached to a tower top flange, a coating of an outer ring of the yaw rotation bearing, and a repair of a lower portion of a nacelle cover.
When the nacelle and the tower are separated for the maintenance work, the nacelle is typically removed from the tower and brought down onto the ground by using a large crane. After that, a desirable maintenance work is performed on the nacelle. However, there are two problems in the procedure of the above maintenance work. The first problem lies in the necessity of many equipment and materials and persons and the necessity of legal preparations (for example, acquisition of a road use permission and the like). This implies that a large expense and a long time period are required for the maintenance work. The second problem lies in the necessity of a wide site in which the nacelle and a wind turbine rotor are located. There is a case that the site necessary for the maintenance work amounts to a square of several tens of meters. This decreases the freedom of the maintenance work. If the maintenance work can be carried out while separating the nacelle and the tower without using the large crane, there are great merits of the reduction in the cost and the improvement of the freedom of the maintenance work, through the simplification of the maintenance work.
Japanese Patent No. 4,699,571 discloses a technique of separating a nacelle and a tower by lifting the nacelle without using a large crane. In the technique described in Japanese Patent No. 4,699,571, a reception stage is attached at the vicinity of the top end of the tower, and a jack is provided on the reception stage. This jack is used to lift the nacelle. However, a work for attaching the reception stage at the vicinity of the top end of the tower is not always easy. For example, when the reception stage is attached to the tower by welding, a work time becomes long for the difficulty of the welding work at a high location. Also, as disclosed in the above reference, a method of tapping a tower top flange to form a female screw and then engaging a bolt with the female screw to attach the reception stage requires a long work time.
As mentioned above, a technical need exists for a maintenance work carried out while separating the nacelle and the tower at a little work amount without using any large crane.